Direct contact air-brine heat exchangers are sometimes used to condition the air in an enclosure by extracting water vapor from the air. An example of such a heat exchanger is in U.S. Pat. No. 4,355,683 wherein concentrated brine is sprayed into a tower with which air from an enclosure is exchanged. The vapor pressure at the air/brine interface of the brine droplets or brine film in the tower is less than the vapor pressure of water vapor in the air at the temperature and pressure of the enclosure air; and as a result, the brine is hygroscopic causing moisture in the air to condense on the brine. Direct contact heat exchangers utilizing this principle are advantageous in greenhouses, for example, as a way to control humidity within the greenhouse during the day when evaportranspiration of plants produce water vapor that would, in the absence of some means of control, produce a humidity approaching 100%, a condition that is unhealthy for the plants.
In conditioning the air in an enclosure using a direct contact heat exchanger of the type described above, concentrated brine from a reservoir is exchanged with the heat exchanger. The brine returned to the reservoir is more dilute than the brine delivered to the reservoir by reason of the absorption of water vapor from the enclosure air contacted with the brine in the heat exchanger. To ensure proper operation, the dilute brine must be reconstituted; and it is conventional to exchange brine from the reservoir with a brine concentrator that evaporates water from the dilute brine thus concentrating it before returning it to the reservoir.
In each brine exchange process, a pump is usually required. Because of the corrosive nature of brine, and its relative viscosity compared to water, specially designed pumps are employed. Such pumps must be constructed of materials compatible with the corrosive brine and usually employ special seals to control leakage. Often, magnetic drives are employed such that the pump is entirely sealed in a housing, and a rotating magnetic field is coupled to the pump to drive the rotor. Not only are conventional pumps for pumping viscous corrosive solutions expensive, as compared with readily available water pumps of the same capacity, but they consume large amounts of power as compared with water pumps of the same capacity. For example, a water pump of a given capacity may cost about $100.00 and consume about 250 watts of power in operation. A comparable pump capable of handling a viscous corrosive brine may cost $500.00 and consume about 600 watts.
It is therefore an object of the present invention to provide a new and improved motor driven pump capable of pumping viscous solutions, such as brine, which is less expensive to manufacture and consumes less power in operation.